CN116292286B - A screw rotor profile for large flow and high pressure differential compression - Google Patents

Abstract

The invention relates to the field of energy and power, and specifically relates to a screw rotor profile used for large-flow, high-pressure differential compression. The gear ratio of the asymmetric male and female rotors is 5:7; the rotor profile is designed to include several segments of continuously derivable ellipses. The curves of arcs, quadratic curves, and arc envelopes; the curvature of the curves in different sections of the screw rotor profile are determined based on the actual working pressure state between the rotor teeth to achieve the machinability of the precision profile and reduce the meshing clearance to improve volumetric efficiency. The overall profile adopts a fluid dynamics design, without the commonly used points, straight lines and cycloids in traditional profiles, avoiding connections similar to sharp points to solve the problem of rotor stiffness caused by high linear speed of the rotor under large flow conditions. and rotor dynamics and other reliability issues.

Description

A screw rotor profile for large flow and high pressure differential compression

Technical Field

The invention relates to the field of energy and power, and in particular to a screw rotor profile for large flow and high pressure difference compression.

Background Art

Twin-screw compressor is a positive displacement compressor that compresses gas by a pair of intermeshing rotors. Tooth profile, also known as profile, is the core technology of twin-screw compressors. Every step forward in screw compressor technology and every improvement in efficiency mainly comes from the innovation of profile technology. Rotor profile is the core and most fundamental technology of twin-screw compressor technology. The end profile of the rotor is composed of multiple different curves, and each pair of intermeshing helical teeth cooperates to complete the gas compression cycle. The end profile of the rotor basically determines the efficiency of the compressor and the stability of the rotor.

The rotor profile has evolved from the initial symmetrical arc to the current asymmetrical complex geometric curve. The development direction of the tooth shape is to increase the area utilization factor by increasing the tooth height radius and reducing the tooth thickness. The traditional profile widely used in air compressors, refrigeration compressors and other fields cannot meet the needs of high-efficiency compression of small molecular weight gases such as helium and hydrogen, nor can it meet the needs of screw operation reliability under large-capacity and heavy-load conditions. The profile not only affects whether the rotor can mesh correctly, but also affects the internal leakage between different axial and lateral pressures, thereby affecting the efficiency of the compressor. The fluid dynamics design of different curves not only affects the resistance loss of gas flow, but more importantly, it affects the stirring work loss of the cooling oil, so the profile design must comply with the laws of fluid dynamics and reduce viscosity losses.

The mathematical geometric configuration of the profile in theory can achieve smooth transitions and various shapes. However, the profile design needs to consider the machinability of the theoretical profile and whether there is sufficient machining accuracy to achieve the theoretical shape under the current industrial level. The machining accuracy often restricts the actual performance of the compressor when compressing small molecular weight gases. Especially for any leaking media, a finer meshing clearance is required to reduce internal leakage losses, and the profile needs to have stronger machinability to ensure machining accuracy. At the same time, the specific geometric structure of the profile needs to consider the actual conditions of the compressed working fluid and operating conditions, which requires the accumulation of a large amount of test data and a continuous optimization process.

In the current field of screw compressors, asymmetric profiles are the traditional mainstream profiles for industrial applications, such as Atlas-X (4:6), Sigma (5:6), GHH (5:6), SRM-D (5:6), GHH (5:6), Hitachi (5:6), etc.

Taking the SRM-D profile as an example, the characteristics, advantages and disadvantages of the traditional profile are introduced. It is developed on the basis of SRM-A. The SRM-A profile adopts five combinations: point-cycloid, straight line-cycloid, pin-tooth arc pair, rolling arc pair, and arc-arc envelope. The tooth curves of the SRM-D profile are all arcs and their envelopes, as shown in Table 1 and Figure 1, which realize the sealing of curved surfaces to curved surfaces between the rotors, reduce the lateral leakage through the contact line, improve the processing performance, and facilitate the use of rolling method. Table 2 summarizes the comparison between the specific composition characteristics of traditional profiles.

Table 1 Characteristics of SRM-D type wire

Female rotor Male rotor Meshing line Female rotor Male rotor Meshing line Arc AB Envelope KL 12 Arc FG Envelope PQ 56 Envelope BC Arc LM twenty three Envelope GH Arc QR 67 Arc CE Arc MO 34 Arc HI Envelope RS 71 Envelope EF Arc OP 45 Arc IJ Arc ST 1

Table 2 Comparison of the characteristics of traditional profiles

The rotor profile of an air compressor or refrigeration compressor is not suitable for compressing small molecular weight gases due to its large meshing clearance. In addition, due to the large number of transitions in the tooth shape, more oil injection is required when operating at high capacity (increased rotor linear speed) or when cooling a working fluid with a larger adiabatic index (such as helium). The traditional profile has an increased loss of stirring oil work, resulting in reduced efficiency, which is manifested as high power consumption and high noise in the compressor.

In the design concept represented by air screw compressors, the traditional rotor profile design principle generally improves reliability by reducing the rotor speed, but the reliability is greatly reduced at high power capacity and large flow, and may even fail to operate normally due to excessive vibration.

On the other hand, as the nominal diameter of the rotor increases, in order to achieve high precision in the processing of precision profiles such as compressed helium, the machinability of the profiles needs to be considered. When compressing helium and hydrogen, the processing accuracy of traditional profiles cannot meet engineering needs because a smaller meshing clearance is required.

Summary of the invention

The embodiment of the present invention provides a screw rotor profile for large flow and high pressure difference compression, so as to at least solve the technical problems that the existing method is prone to cause leakage of working fluid resulting in reduced efficiency and reduced rotor dynamics stability due to high rotor linear speed.

According to one embodiment of the present invention, a screw rotor profile for large flow and high pressure difference compression is provided, which is designed by the following steps, including:

The screw rotor profile is designed to include a number of continuously derivable elliptical arcs, quadratic curves, and arc envelope curves; the screw rotor profile adopts an asymmetric streamlined design with a positive and negative rotor ratio of 5:7;

The curvature of the curves in different sections of the screw rotor profile is determined in combination with the actual working pressure state between the rotor teeth.

Furthermore, the screw rotor profile is a plurality of elliptical arcs and parabolic curves with different curvatures that are smoothly transitioned and tangentially connected.

Furthermore, the curvatures of different sections in the screw rotor profile are adjusted according to different gas pressure distributions during the micro-element compression process between the teeth.

Furthermore, in the high-pressure area, the screw rotor profile is relatively gentle; in the low-pressure area, the curvature of the profile curve is increased to ensure close meshing between the male and female rotors.

Furthermore, the screw rotor profile is designed to include 7 segments of continuously differentiable elliptical arcs, quadratic curves, and circular arc envelope curves.

Furthermore, the meshing clearance between the male and female rotors is 10-30 μm.

Furthermore, the meshing clearance is controlled to be 10-20 μm when helium is compressed.

Furthermore, the rotor circumferential speed is 30-75 m/s.

Furthermore, the screw rotor is suitable for working fluids such as helium, hydrogen, hydrogen sulfide, air, and refrigerant.

Furthermore, the applicable working conditions of the screw rotor are: rotor aspect ratio 1.0-1.75, intake pressure 30kPa-500kPa, single-stage suction and exhaust pressure difference 300kPa-2000kPa, and single-unit gas transmission capacity 800m ³ /h-13000m ³ /h.

The screw rotor profile used for high flow and high pressure difference compression in the embodiment of the present invention is designed as a curve including several segments of continuously derivable elliptical arcs, quadratic curves, and arc envelopes; the curvature of the curves in different sections of the screw rotor profile is determined in combination with the actual working pressure state between the rotor teeth. The overall profile adopts fluid dynamics design, without the points, straight lines and cycloids commonly used in traditional profiles, avoiding the connection similar to the sharp point, so as to meet the reliability requirements brought by the high linear speed of the rotor under large flow conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

FIG1 is a diagram showing the composition of each segment of the SRM-D profile curve in the coordinate system of the prior art and the meshing line diagram of the yin and yang rotors;

FIG2 is a diagram of the global coordinate system and the local coordinate system used in the mid-line design of the present invention;

FIG. 3 is a specific diagram showing the geometric curves of each segment of the profile of the present invention.

DETAILED DESCRIPTION

In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

The present invention is mainly used to solve the problems of high linear speed (30-75m/s) caused by large rotor diameter, increased internal leakage rate under pressure difference drive, and greater rotor dynamics caused by heavy-load rotor stiffness and dynamic balance faced by screw compressors under large flow and high pressure difference conditions. While increasing the meshing clearance of the male and female rotors, in order to improve the rotor stiffness and strength, more teeth are used and the difference in the number of teeth between the male and female rotors is increased. The number of teeth and the difference in the number of teeth of the rotor are precisely designed to improve the utilization coefficient of the profile area and the rotor dynamics characteristics (i.e., improve the rotor stability), which is reflected in the reduction of vibration and noise during actual operation, and the extension of the maintenance-free period.

In order to realize the machinability of the precision streamlined profile, the present invention proposes a new profile with an asymmetric male and female rotor tooth ratio of 5:7, and the rotor nominal diameter is consistent. Compared with the traditional profile, it has better machinability and rotor dynamics characteristics; due to the large number of teeth and large difference in the number of teeth, the area utilization factor is improved, and the stability of the rotor under heavy load conditions (large pressure difference, large flow) and the volumetric efficiency of the compressor are also improved.

This profile is made up of several elliptical arcs and parabolas with different curvatures, which are smoothly transitioned and tangently connected. The overall profile adopts fluid dynamics design, without the points, straight lines and cycloids commonly used in traditional profiles, avoiding the connection similar to sharp points, so as to adapt to the reliability requirements brought by the high linear speed of the rotor under large flow conditions. The curvature of different sections is adjusted according to the different air pressure distribution in the process of micro-element compression between teeth. In the high-pressure area, the profile is relatively flat and it is easier to achieve processing accuracy; in the low-pressure area, the curvature of the profile curve is increased to ensure the close meshing between the male and female rotors, and the meshing gap is controlled at 10-25μm to reduce the leakage of small molecular weight gases such as hydrogen and helium.

This type of line is mainly suitable for: inlet pressure 0.03-1.0MPa, single unit gas output ^800-13000m3 /h, rotor aspect ratio between 1.0-1.75; applicable working fluids include hydrogen, helium, propylene, ammonia, freon, air, etc.

The new type of line of the present invention is a further development on the basis of the traditional type line. It is suitable for machining rotors by grinding method and can achieve higher precision than rolling processing, so it is better suitable for high-efficiency compression of small molecular weight gas and large capacity and high pressure difference operation conditions. It is necessary to avoid sharp points, arcs with very small radius, straight line segments, etc. The area utilization factor is improved by increasing the tooth height radius, reducing the tooth thickness and increasing the number of teeth. The internal leakage loss between high and low pressure is reduced by further reducing the meshing clearance and leakage triangle. Better fluid dynamics design reduces the oil and gas flow work loss and further improves the efficiency and reliability of the compressor.

The twin-screw compressor uses a male rotor to drive the female rotor to move. Stability requires stable transmission between the male and female rotors, which means that the rotors maintain a certain direction during operation. If the torque direction changes, it will cause collisions between the rotors on the contact line, which will cause vibration, wear and noise. The SRM-D type line tooth shape has this change in torque direction, especially on rotors with large flow and large diameter. The new line of the present invention takes this factor into consideration when designing the tooth curve, thereby improving the stability of the rotor operation.

In order to meet the working conditions of large flow and high pressure difference (when the working fluid leakage is more serious), the present invention changes the curvature of the profile (i.e., the geometric configuration) according to the specific pressure distribution law of the rotor profile, and improves the machinability and machining accuracy of the profile. The new line has a smaller meshing gap and additional oil flow work loss, thereby improving the compression efficiency, which not only meets the needs of large-scale cryogenic projects, but also improves efficiency and stability in the fields of large-capacity commercial refrigerator compressors, process gas compressors, etc.

The profile of the present invention is composed of 7 segments of continuously differentiable elliptical arcs, quadratic curves, circular arc envelopes and other curves; the curvature of the curves in different sections is determined in combination with the actual working pressure state between the rotor teeth, rather than solving a separate mathematical meshing equation. That is: in the opening direction of the high-pressure end of the profile, the profile curvature is reduced, and the profile tends to be flatter, ensuring the processing accuracy; because the larger and steeper the profile curvature, the more difficult it is to control the processing accuracy. In the closing direction of the low-pressure end of the profile, since the profile tends to be flat, the profile angle is appropriately increased to reduce the meshing clearance of the male and female rotors, thereby reducing the internal leakage loss under high pressure difference. The technical solution of the present invention includes:

The ratio of male to female rotors is 5:7, and the number of female rotor teeth is increased, which increases the actual gas transmission volume and rotor stiffness (adapting to gas forces under large flow and high pressure difference); the gear ratio and gear difference are increased to make the rotor force uniform, and the stiffness is 2-4 times that of other gear ratios. Since the pressure difference between the unit volumes is relatively reduced, the lateral gas leakage under high pressure difference conditions is reduced;

The meshing clearance between the male and female rotors is 10-30μm, and the meshing clearance is generally controlled at 10-20μm when compressing helium;

The main applicable working fluids are helium and hydrogen, and can also be extended to process gases such as hydrogen sulfide and refrigerants such as air and Freon;

Applicable working conditions: rotor aspect ratio 1.0-1.75, intake pressure 30kPa-500kPa (absolute pressure), single-stage suction and exhaust pressure difference 300kPa-2000kPa, single unit gas transmission capacity 800m ³ /h-13000m ³ /h;

Rotor circumferential speed: 30-75m/s.

The technical solution of the present invention is described in detail as follows:

1. Basic characteristics of the profile

The profile of the present invention is composed of 7 sections of continuously derivable elliptical arcs, quadratic curves, circular arc envelopes and other curves; the specific geometric configurations of the curves in different sections are determined by the actual working pressure state of the rotor.

FIG2 shows the global coordinate system and the local coordinate system used in the profile design of the present invention; FIG3 shows the geometric structure of the profile of the present invention.

The specific characteristics of each curve segment are given in Appendix 3 (the 7 curve segments corresponding to the negative rotor are the conjugate curves of each curve segment of the positive rotor).

Table 3 Specific characteristics of the 7-segment curve of this type line

As shown in Table 3 and Figure 3, the profile of the present invention is composed of 7 segments of continuously differentiable curves and is uniquely determined by 21 characteristic parameters, including A0, Z1, Z2, R1, R2, R3, R4, AA1, BB1, AA2, BB2, s, t, AY, φ1, φ2, α, φ3, φ4, φ5, and θ1.

Where A0 is the center distance between the male and female rotors;

Z2 and Z1 are the number of teeth of the male and female rotors respectively;

R1, R2, R3, and R4 are arc radii at different stages (R2 and R4 are on the female rotor);

AA1, BB1, AA2, BB2 are the lengths of the major and minor axes of the elliptical arcs at different segments;

s and t are two parameters of the quadratic curve;

AY is the distance between the starting point A and the y-axis;

φ1, φ2, α, φ3, φ4, φ5, θ1 are the curve angle parameters of different sections.

The present invention also includes:

Asymmetric profile with a male-female rotor gear ratio of 5:7;

The meshing clearance between the male and female rotors is 0.010-0.030mm;

Rotor circumferential speed: 30-75m/s, also reduces the internal leakage rate of the working fluid;

The main applicable working fluid is helium, and it can also be extended to hydrogen, hydrogen sulfide and other process gases and air, refrigerants;

Applicable working conditions: Inlet pressure 30kPa-500kPa (absolute pressure), single-stage suction and exhaust pressure difference 300kPa-2000kPa, single unit gas transmission capacity 800m ³ /h-13000m ³ /h.

2. Specific coordinates of the embodiment line

The present invention provides specific geometric coordinates of the profile by determining 21 parameters and the curvature and meshing clearance value of each segment of the curve, with 514 points of the male rotor and 510 points of the female rotor in the embodiment shown in Table 4. The gear ratio of the male and female rotors is 5:7, the meshing center distance is 164 mm, and the rotor contact line is the spiral line formed by the tangent points of the male and female rotor pitch circles.

Table 4 Coordinates of the profile of the male and female rotors in the example (unit: mm)

The key points and points to be protected of the present invention are at least:

1. The profile of the present invention is composed of 7 sections of continuous and derivable curves, and adopts an asymmetric streamline profile with a male-female rotor ratio of 5:7;

2. The meshing clearance between the male and female rotors is 10-30μm;

3. Rotor linear speed: 30-75m/s;

4. Rotor aspect ratio 1.0-1.75;

5. The main applicable working fluid is helium, and it can also be extended to process gases such as hydrogen and hydrogen sulfide, as well as air and refrigerants;

6. Applicable working conditions: Inlet pressure 30kPa-500kPa (absolute pressure), single-stage suction and exhaust pressure difference 300kPa-2000kPa, single unit gas transmission capacity 800m ³ /h-13000m ³ /h;

7. Specific geometric curves of the embodiment profile (group of points of the male rotor 514 and the female rotor 510) and their proportionally enlarged and reduced geometric features;

Compared with the prior art, the invention has the following advantages:

In view of the problems of large meshing clearance, reduced efficiency, increased vibration and noise, poor rigidity and low strength of the yin and yang rotors, complex processing and high cost of the traditional screw line under large flow conditions, a new rotor line suitable for high-speed operation is proposed:

1. The asymmetric design of the male and female rotors is 5:7, and the rotor stiffness is 2-4 times that of other gear ratios, which improves the rotor dynamic stability;

2. The profile geometry consists of 7 segments, and the curvature of each segment is determined according to the actual pressure distribution, which improves the processability and processing accuracy of the profile;

3. The meshing clearance is refined to 10-30μm, which improves the volumetric efficiency;

4. High rotor circumferential speed: 30-75m/s; (the circumferential speed of the traditional rotor is generally 15-25m/s);

5. The geometric characteristics of the profile can still reduce the oil and gas flow work loss under large flow and high pressure difference conditions at high speed.

The present invention has been tested on a test prototype, and the experimental test results show that under rated conditions, the volumetric efficiency reaches 92.4%, the adiabatic efficiency reaches 84.9%, and the isothermal efficiency reaches 61.4%. The main parameters are all at the highest level of international products under the same working conditions (power, mass flow rate and suction and exhaust pressure) (i.e., volumetric efficiency 80.4-83%, adiabatic efficiency 72.6-78.1%, isothermal efficiency 52.9-56.7%).

The modified design of the present invention includes:

1) Intercept the tooth profile coordinate points and change the ratio of the male and female rotors;

2) Enlarge or reduce the model line in proportion.

The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the system embodiments described above are only schematic. For example, the division of units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed over multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk, etc., various media that can store program codes.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. A screw rotor profile for large flow and high pressure differential compression, which is characterized in that it is designed by the following steps, including: The screw rotor profile is designed as a curve including several continuous and derivable elliptical arcs, quadratic curves, and arc envelopes; the screw rotor profile adopts an asymmetric streamlined design with a masculine and feminine rotor tooth ratio of 5:7; The curvature of the curves in different sections of the screw rotor profile is determined based on the actual working pressure state between the rotor teeth; The profile line includes a first arc, a first elliptical arc, a first arc envelope, a second arc, a second arc envelope, a second elliptical arc, and a quadratic curve that are connected in sequence. 2. The screw rotor profile for large-flow and high-pressure differential compression according to claim 1, characterized in that the curvature of different sections in the screw rotor profile is determined by the presence of different air pressures during the inter-tooth micro-element compression process. distribution to adjust. 3. The screw rotor profile for large-flow high-pressure differential compression according to claim 2, characterized in that in the high-pressure area, the screw rotor profile is relatively gentle; in the low-pressure area, the curvature of the large line curve is increased to ensure the yin and yang. The rotors are tightly meshed. 4. The screw rotor profile for large flow and high pressure differential compression according to claim 1, characterized in that the meshing gap between the male and female rotors is 10-30 μm. 5. The screw rotor profile for large flow and high pressure differential compression according to claim 4, characterized in that the meshing gap is controlled at 10-20 μm when compressing helium gas. 6. The screw rotor profile for large flow and high pressure differential compression according to claim 4, characterized in that the rotor circumferential linear speed is 30-75m/s. 7. The screw rotor profile for large flow and high pressure differential compression according to claim 1, characterized in that the applicable working fluids of the screw rotor are helium, hydrogen, hydrogen sulfide and air. 8. The screw rotor profile for large flow and high pressure differential compression according to claim 1, wherein The characteristic is that the screw rotor is suitable for working conditions: rotor aspect ratio 1.0-1.75, air inlet pressure 500kPa, The single-stage suction and exhaust pressure difference is 2000kPa, and the gas transmission capacity of a single unit is 800m ³ /h-13000m ³ /h.